Muzzle pressure indicator



April 25, 1944. GAR ND 2,347,188

MUZZLE PRESSURE INDICATOR Filed April 2, 1942' LI uhn C B a f'an d WW4 I Patented Apr. 25, 1944 UNITED STATES PATENT OFFICE MUZZLE PRESSURE INDICATOR John 0'. Garand, Springfield, Mass. Application April 2, 1942, Serial No. 437,369

(Granted under the act of March a, 1883, as amended April so, 1928; 370 o. c. 757) 3 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a pressure indicating apparatus particularly adapted to the measurement of the gas pressure within the barrel of a firearm.

,It is an object of this invention to provide an improved apparatus for measuring or indicating a. fluid pressure of large magnitude but exceedingly short duration. It is a further object of this invention to provide an apparatus for measuring or indicating the gas pressure developed in the barrel of a firearm after the discharge of a cartridge.

A particular object of this invention is to provide a compact and readily portable apparatus for indicating the relative gas pressure developed by various cartridges in a testing barrel, particularly at the muzzle end of the barrel.

Devices for measuring the gas pressure developed in firearms are known in the art, however, such devices generally utilize an apparatus wherein a deformity is produced in a soft metal by the force of the gas pressure to be measured, the extent of the deformity indicating the magnitude of the gas pressure development. Such devices have been utilized primarily for the indication of gas pressure developed at the chamber end of the barrel of the firearm. Apparently, no successful practical device has been known which provides an indication of the gas pressure at the muzzle end of the barrel of a firearm.

The measurement or indication of the gas pressure at such point presents entirely different problems than those encountered in the measurement of gas pressure at the breech end of the barrel. It can be readily appreciated that the maximum gas pressure at the muzzle end of the barrel is relatively small compared with the maximum gas pressure at the breech end. Furthermore, such pressure at the muzzle end exists for a much shorter duration of time. The duration of such pressure at the muzzle end is measured by the time of traverse of the bullet from the point of pressure measurement to the end of the barrel. In fact, in a gas actuated rifle such as disclosed in my previous U. S. Patent No. 1,892,141, the point at which it is desirable to determine the gas pressure is located approximately an inch and one-half from the end of the barrel, hence the time available for pressure measuringapparatus to operate is that time required for the bullet to traverse one and onehalf inches at the end of the barrel.

Irrespective of the foregoing detrimental factors, a pressure indicating apparatus embodying the features of this invention will nevertheless produce a reliable and accurate indication of the relative gas pressures developed at the muzzle end ofthe barrel by various cartridges.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing in which:

Fig. 1 is an external view of an assembled muzzle pressure indicator constructed in accordance with this invention.

Fig. 2 is a cross-sectional view of Fig. 1 taken along the line 2-2 prior to firing a cartridge.

Fig. 3 is a cross-sectional view of Fi 1 taken along the line 22 after firing a cartridge.

Fig. 4 is a partial longitudinal sectional view of the forward portion of Fig. 1.

Fig. 5 is a cross-sectional view of Fig. 1 taken along the line 3-3.

As shown in Figure 1 in assembled relation, the pressure indicating apparatus comprises a testing barrel A, a firing mechanism (not shown), and a pressure measuring apparatus C. The barrel A is preferably provided with the same interior configuration and dimensions as the particular rifle for which it is desired to measure the pressure developed at the muzzle end. The chamber end of the testing barrel A is provided with a threaded portion 5 which engages the firing mechanism (not shown). Although any firing mechanism may conveniently be used, the receiver assembly of the U. S. rifle, caliber .30 M1903 may be conveniently utilized. Adjacent to the chamber of the testing barrel, an enlarged diameter portion D is provided which rests in a suitable supporting member such as the trough of a channel iron E.

A small porthole I0 is provided near the end of the testing barrel at the point where it is desired to obtain an indication of the gas pressure developed. This porthole I0 will bypass a portion of the gas developed in the cartridge discharge during the time that the bullet is traversing the distance from the porthole to the end of the barrel. If the location and dimension of the porthole ID are made identical with the location and dimension of the gas port of the rifle disclosed in my U. S. Patent No. 1,892,141, it is apparent that the gas pressure indications obtained by this apparatus will closely approximate the pressure (leveloped in that rifle by similar cartridges. The gas port I connects directly with a larger cylindrical chamber II also provided in barrel A.

A base member I of the measuring apparatus C is provided with a cylindrical opening I5a by which it is mounted on barrel A in the vicinity of the gas port Ill. The base member I 5 is provided with two opposed angular side surfaces I 5d and I5e. These surfacesz each lie within planes that are mutually perpendicular and which also are tangent to the surface of the enlarged diameter portion D of the barrel. With this configuration, the entire apparatus is readily supported by laying it in the trough of a length of angle iron I The base member I5 and the enlarged diameter portion D are not secured to the angleironE in order to permit the entire apparatus to be :slidably moved into any desired position within the trough thereof. 4

A cylindrical opening I 5b is provided in the base I 5 of the same dimension-amend in direct align ment with, thec'hamber liin the barrel. A hollow cylindricalrmember M is fitted into opening I5b and eharnber I I thus anchoring the base I5 with'respect to the barrel A. The interior surface of the member I 4 definesa smooth bore overlying the gas port I0.

A longitudinal piston member I 'I--is arranged to reciprocate in-the cylindricalbore of the member I4. The piston member I! is of greater length than the cylindrical member I4. On the-extending part of piston member I1 an increased diameter band I8 is provided. A hollow cylindrical fitting I3 is provided which-surrounds the extending portions of the pistonmember IT. The lower surface of the fitting I3 is seatedin a recess I50 provided in the base member I5. In this position the'baseoffitting I3 engages the top of the cylin 'der member I4 and preventsthe' Withdrawal of the member I4 fromthe'opening' I511 and'the chamber! I. The'fitting' I3 is securely fastened to base I5 by screws I6. 'Fittin'g'l3 is further provided'with inwardly extended portion I9 which not only limits the upward movement of piston member I! through engagement with the top.

shoulder'ofband 'I8 but alsoserves'to vertically guide the movementfof'the piston member H by snugly engaging the end of the piston member. The downward movement of the piston member I 1' is lilnited'by engagement of the bottom shoulderof band I8 with the top of cylindrical member I. The'piston member I'I should be made of a very hard metal or by other means provided with an'ex'tremely hard metallic topsurface 2I. The dimensionof the piston member is such relative tothe fitting I3 that'w-hen the. piston member I! is at 'its' lowermost position, its top surface 2I- is coplanar with the top surface of the fitting I3.

The base member I5. also-serves to support two vertically extending slide members 25 and 26. These'members are of circular cross-section and are fitted into holes 22 and 23 respectively in base member I5. fSe't screws 2'! serve to anchor the slide members to the base.

'A weight member2 8-is arranged to freely vertically'slide on members 25 and 'lfi by engagement of these members in the circular holes 29 and3il therein. The weight member is-prefera-bly composed-of a very hard metal and its lower surface contactsthe hard top surfaceZl of the piston member II when the weight 28 is in its lowermost position. Alternately, an insert of hard metal may be provided within the weight member '23 so asto contactthe topsurfacezl.-of-piston member weight member 28.

To operate the pressure indicating apparatus, the weightmember 28 is lowered on the slides 25 and 26 so that it is resting upon the hardened top surface 2I of piston member I1 and the ring 33 is lowered 'to rest on the weight. A cartridge is then fired through the barrel A in a conventional manner by theelements of the firing mechanism .(not shown). When the projectile has passed the port II], the exploded gases enter the port and contact the' bottom surface of piston member IT. The pistonmember will thus receive :a large impact force by the action of the gas. This force, however, will exist only dur-ingthe time that the "projectile is traversing the distance between the port I i] and'theendof the barrel.

The-impact fOrce received by the piston- IT is transmitted to the weight member 28 through the coaction of the hardened piston surface 2| with the hardened base of the Weight. By the use 'of such hardened surfaces, the elastic energy losses will be'kept at a minimum. The impact causes the member 28 to rise upward on the slide members25 and EEcarrying with it the ring 33. The sliding surfaces are suitably lubricated to "keep frictional losses at a minimum. The energy imparted to'the weight memberis transformed in the vertical rise of the-weightmember'whereafter it falls back to its initial position. However, the ring "33 remains in its maximum height position on the slide member and thusserves to indicate the maximum'height reached by the weight mem- -ber 28. Graduations-34 may be provided on the slide member 25 or 26 to conveniently measure the *heightreached by the'ring 33.

Knowing the mass of weight member 28,'the maximum height which it reached and the time during which the gas pressure forces were acting, the magnitude of the average gas pressure may be determined by conventional mathematical methods. Itis possible to graduate the height reached by the ring 33 in terms of pressure'developed by the gas. Even-without calibration of the height reached by the ringand hence by weight member '28, the device provides a veryconvenient arrangement fcr'determining relative pressure developed by different cartridges fired through" the testing barrel A. The various heights reached-by the ring 33 would indicatethe relative pressures developedbythe various cartridges since allother factors in the apparatus are substaritiallyconstant.

Theembodiment of my inventionas heretofore described operates very satisfactorily in the measurement-0f pressures of the magnitude encountered near the end-of the muzzle. If it-is desired terneasurezthe' higher pressures existing in the barrel in theregions near the chamber,- it is'possible to dose merely by increasing the size 'of the weight member 28 so as-to keep its upward 'move ment within the limits 0f' the slide member 'and/ or by making theslide members longer.

=Iclaim: r 1.--A device for measurement of short duration gas pressures comprising a cylinder arranged to receive a portion of such gas, a piston mounted in said cylinder, a weight mounted for movement independently of said piston, said weight arranged to lie against said piston and arranged to be struck an impact blow by said piston acting under the force of said gas and means for indicating the extent of movement of said weight after said impact.

2. A device for measurement of short duration gas pressures comprising a cylinder arranged to receive a portion of such gas, a piston mounted in said cylinder, a weight mounted for vertical movement independent of said piston, said weight arranged to lie against said piston and to be struck an upward impact blow by said piston acting under the force of such gas and means for indicating the height reached by said weight after said impact.

3. A device for measurement of gas pressure developed by a firearm cartridge within a barrel comprising a base member arranged to surround the barrel, vertical guide members mounted in the base member, a weight mounted for vertical movement on the guide members, a cylinder chamber in the base member means arranged to supply a portion of the gases developed within the barrel to said cylinder chamber, a piston mounted in said cylinder chamber and arranged to abut the base of said weight whereby energy imparted to said piston by the gas is transmitted by impact to the weight, raising it a measurable distance, and means for indicating the maximum height reached by said weight.

JOHN c. GARAND. 

